Where do I go from here?

I have just received a so called notice of intended prosecution for an alleged speeding offence by a manned camera, for the alleged offence of doing 45 in a 30 speed zone.

Now i cannot definately state that i was not over the limit , but i was on my way to work and never rush there (who would) but is it a case of my word against theirs? where i do i go from here? or should i just hold my hands and accept it?